The present invention relates to a method for enhancing the visual effect of a three-dimensional molded part using in-mold labeling and the label used therewith, particularly a method and label for enhancing the three-dimensional visual effect of raised surfaces on a blow molded article.
It is well known to apply conventional paper and plastic film labels to two-dimensional surfaces of blow molded plastic articles, such as shampoo bottles and beverage containers, after the part has been removed from the mold. To improve the efficiency of blow molding operations, transfer machines were developed which place labels on the blow mold itself before the plastic part is formed. When the plastic article is blow molded, the label either melts or adheres to the two-dimensional container surface.
U.S. Pat. No. 5,266,377, issued to Kinoshita et al., discloses a label and method for applying a label during in-mold molding. The label comprises a printed layer formed on a surface of a non-oriented plastic based film over which a membrane layer is overlapped. The label is inserted into a mold for in-mold labeling and is held in the proper position on the mold using vacuum suction or static electricity. Plastic is then injected into the mold and the membrane layer on the label bonds to the plastic article.
U.S. Pat. No. 5,223,315, issued to Katsura et al., discloses a label for two-dimensional surfaces consisting of a base of stretched film having a thermal shrinkage ratio greater than the mold shrinkage ratio of a plastic constituting the outer surface of a container. Using materials that satisfy these ratios prevents creasing and swelling of the label on containers with polyolefin outer surfaces.
U.S. Pat. No. 5,256,365, issued to Gordon et al., discloses a method of placing a label on mold cavities in a blow molding machine using an in-mold labeling system including first and second magazines with rotary members and vacuum assist.
U.S. Pat. No. 5,639,536, issued to Yamazaki et al., discloses the method of applying a transfer layer having projections and recesses finer than those on a molded part to produce a matte surface with good wear characteristics. The recesses on the molded part are up to approximately 300 microns deep and present therefore, essentially a two-dimensional surface.
The above-mentioned patents work satisfactorily for molded articles with thin walls, such as two-liter plastic beverage bottles and shampoo containers having wall thicknesses of approximately 0.015 to 0.060 inches. These articles retain relatively little heat in the walls compared to thick-walled molded articles, such as cases for power tools, which typically have wall thicknesses of approximately 0.055 to 0.250 inches. Thick-walled articles require a different label capable of withstanding the increased heat retained and subsequently released from the thick-walled sections. Moreover, the above-described background art is generally limited only to a two-dimensional surface and does not enhance the appearance of three-dimensional surfaces.
What is desired, therefore, is a label for in-mold labeling of plastic parts which is capable of being in a mold cavity therefore taking on the three-dimensional appearance of the relieved features or the entire molded product, and which is capable of being used in in-mold labeling operations on thick-walled molded parts which retain a substantial amount of heat in the thick walls. In another aspect, what is desired is a method of enhancing the three-dimensional appearance of a raised surface on a plastic part using an in-mold label.
Accordingly, it is an object of this invention to provide a label for in-mold labeling of plastic parts that is capable of being in a mold cavity therefore taking on the three-dimensional appearance of the relieved features or the entire molded product.
Another object of this invention is to provide a label which is capable of being used in in-mold labeling operations on thick-walled molded parts which retain a substantial amount of heat in the thick walls.
Yet another object of this invention is to describe a method of enhancing the three-dimensional appearance of a raised surface on a plastic part using an in-mold label.
In one embodiment of the present invention, the label itself comprises a printed plastic, such as polypropylene or polyethylene, having a background and lettering and/or one or more patterns such as photo graphics, a heat-activated adhesive layer on the bottom surface thereof for adhering to the molded article, and a surface layer, such as varnish, on the top surface to insulate the core from the cool mold cavity and/or protect the printed core from damage.
To apply the label, the label first must be positioned on the mold surface using a transfer system, mechanical tooling components, or by hand. The label is precisely held in place on the mold surface by vacuum suction and/or static electricity. A parison, the semi-solid, molten, plastic xe2x80x9ctubexe2x80x9d that is extruded from the blow molding machine, is dropped between the mold halves. The mold then closes around the parison and air is injected into the parison forcing the parison to take the shape of the mold cavity, i.e., the finished molded part, including any relief cut into the mold cavity. The label is also forced to stretch and take the shape of the cavity relief or part contour by the plastic parison resulting in an enhanced three-dimensional visual effect of the raised article surface. The heat from the parison causes the heat-activated adhesive layer to bond to the molded part.
In another embodiment, the label comprises a plastic core, such as polyethylene or polypropylene, and a surface layer, such as a varnish coating. In this embodiment, when the plastic parison is blown and contacts the label, the heat from the plastic causes the bottom surface of the plastic core to melt and permanently bond to the parison.
The invention and its particular features and advantages will become more apparent from the following detailed description considered with reference to the accompanying drawings.
FIG. 1 is a cross sectional view of a label in accordance with the present invention;
FIG. 2 is a plan view of the label of FIG. 1 showing the lettering which may be raised to produce a three dimensional effect;
FIG. 3a is a perspective view of one mold cavity used to produce the label of FIG. 1 illustrating the cavity relief; and
FIG. 3b is a perspective view of a molded part manufactured from the mold cavity illustrated in FIG. 3a. 